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Technical Description
The power supply regulates the battery voltage and pr5Vdc to the microcontroller and
all circuitry apart from the audio power amplifier which is supplied directly from the battery. The
power supply is activated by the on/off switch. The supply is firstly turned on by the on/off
switch and then the microcontroller takes over and keeps the power supply on, turning the
supply off when the auto shut off time has elapsed or the on/off switch is depressed a second
time.
Power Supply
This resets the master microcontroller whenever the unit is switched on. The slave
microcontroller is reset by the master microcontroller.
Power On Reset
The probe identification feature is used to automatically select the operating mode, depending
on the probe type and in the SD2-P, MD2-P and RD2, to automatically scale the waveform
output. The probe identification circuit detects the DC level on the output from the probe thus
determining the type of probe fitted.
Probe Identification
The battery monitor circuit enables the microcontroller to assess the battery voltage by
comparing this to a reference voltage.
Battery Monitor
Active noise reduction is a technique used to reduce the amount of noise or "hiss" depending
on signal level.
When a large signal has been detected the cut off point of the filter is moved so that there is no
reduction in high frequency content of the signal. When the signal level is low, or no longer
present the filter is switched in to reduce the high frequency hiss.
Active Noise Reduction (ANR)
The soft limiter reduces the level of any harsh overload signals that may occur, for example,
when the probe is moved.
Soft Limiter
The active noise reduction system relies on the control signal from the sensing circuitry. The
filter response is dependent on the control signal level.
Active Noise Reduction Sensing
The audio power amplifier drives the loudspeaker or headphones. The input level is set by the
volume control.
The output signal is fed to the loudspeaker, via the switched headphone socket. On start up
there is a delay in the supply of power to the audio amplifier. This allows the circuit to stabilise.
Audio Power Amplifier